Te Papa will not go through with buying the singlet earlier believed to have been worn by Peter Snell at the 1964 Olympics because it is not authentic, the national museum says.
Te Papa had the winning bid of $122,500 at the auction last week for the singlet, which had previously been expected to sell for up to $30,000. The buyer's premium would have meant the museum would pay a total of $140,875.
At the time, chief executive Rick Ellis said the singlet told New Zealanders much about their history.
But this morning he announced the museum did not believe it was the singlet worn by Sir Peter in the 800m and 1500m races in Tokyo, for which he won gold medals.
"We believe the item was offered for sale in good faith, but our inquiries have shown that the singlet is not the one worn by Peter Snell at the 1964 Tokyo Olympic Games," Mr Ellis said.
"We are very disappointed and we know the public will be too."
Speaking from his home in Texas, Sir Peter, 77, said he thought the actual singlet would have been a nylon polyester fabric, and it had turned out the one bought at auction was cotton.
"I can't even really remember what happened to the [singlet]. I would have thought that I would have at least kept one of them, and in fact I'm going to have a good look around here as you say, turn the place upside down and see if I can find something."
Te Papa spokeswoman Kate Camp confirmed to Nine to Noon that the fabric on the singlet was not what would be expected from the Tokyo Olympics.
"The day after the auction one of the curators in our team raised a question mark about it. [Auction house] Cordy's have been very helpful to us, they've been able to take the singlet away and do some further analysis.
"I don't think we'll ever know the origins of it - you can imagine how an item like this might come about, perhaps created as a replica."
It was not a safe assumption to make that it was a fake, she said.
Cordy's owner Andrew Grigg, said the seller obtained the top about eight years ago and believed it to be authentic. The auction house had researched it and also believed it was real, he said.
Ms Camp said an independent expert was now investigating the acquisition process.
What about the medals?
Sir Peter said at the time of the auction he did not remember giving the singlet away, but probably had done for a charity event many years ago.
"I'd actually accused my ex-wife of dumping it before she left New Zealand to join me in the United States and she said 'oh no no no I never did that', so it might have been one of those things I have given to be auctioned off for a charity and someone bought it way, way back," he said.
After the auction, Sir Peter said he would consider gifting the gold medals he won in 1964 to the museum, since it had the singlet, and paid so much for it.
However, he had previously said he hoped the singlet would end up at New Zealand Sports Hall of Fame in Dunedin, and had intended to donate his medals there.
Sir Peter said today that initially he had not even thought about Te Papa as a place to give the medals. But now he knew they dealt with sports memorabilia he would think carefully about giving the medals to the museum.